System and method for eliminating bell tap on analog telephones

Claim 1

A device for generating a signal for use in a telephone system, the signal comprising one or more AC cycles and one or more DC cycles, being biased by a bias voltage, comprising: a first means for generating an AC signal; a second means for generating a DC signal; and a third means, controlling said first and second means, for producing a composite ac/dc signal, comprising said AC signal and said DC signal alternately spaced in time, said third means comprising: a fourth means for determining when one of the AC cycles is complete; a fifth means, coupled to said fourth means, for determining when a voltage of said AC signal is equal to the bias voltage when said AC cycle is complete; a sixth means, coupled to said fifth means, for generating a portion of said composite signal from the bias voltage level to a DC voltage level with a first overall slope, the absolute value of said first slope being less than the maximum absolute value of the slope of said AC signal; and a seventh means, coupled to said sixth means, for generating a portion of said composite signal from said DC voltage level to the bias voltage level, with a second overall slope, the absolute value of said second slope being less than the maximum absolute value of the slope of said AC signal.

Claim 2

A device for generating a signal for use in a telephone system, the signal comprising one or more AC cycles and one or more DC cycles, being biased by a bias voltage, comprising: a first means for generating an AC signal; a second means for generating a DC signal; and a third means, controlling said first and second means, for producing a composite ac/dc signal, comprising said AC signal and said DC signal alternately spaced in time, said third means comprising: a fourth means for determining when one of the AC cycles is complete; a fifth means, coupled to said fourth means, for determining when a voltage of said AC signal is equal to the bias voltage when said AC cycle is complete; a sixth means, coupled to said fifth means, for generating a portion of said composite signal from the bias voltage level to a DC voltage level with a first overall slope, the absolute value of said first slope being less than the maximum absolute value of the slope of said AC signal; and a seventh means, coupled to said sixth means, for generating a portion of said composite signal from said DC voltage level to the bias voltage level, with a second overall slope, the absolute value of said second slope being less than the maximum absolute value of the slope of said AC signal.

Claim 5

A method of generating a signal for use in a telephone system, comprising the steps of: (1) generating an AC signal; (2) determining a first time T1 when a voltage of said AC signal is equal to a given bias voltage when a ring cycle is complete; (3) ramping said AC signal from said bias voltage level, beginning at said time T1, to a DC voltage level at a slope whose absolute value is less than the maximum absolute value of the slope of said AC signal; (4) generating a DC signal and determining a second time T2 when a message waiting cycle is complete; and (5) ramping from said DC signal from said DC voltage level, beginning at said time T2, to said bias voltage level at a slope whose absolute value is less than the maximum absolute value of the slope of said AC signal.

Claim 6

A method of generating a signal for use in a telephone system, comprising the steps of: (1) generating an AC signal; (2) determining a first time T1 when a voltage of said AC signal is equal to a given bias voltage when a ring cycle is complete; (3) ramping said AC signal from said bias voltage level, beginning at said time T1, to a DC voltage level at a slope whose absolute value is less than the maximum absolute value of the slope of said AC signal; (4) generating a DC signal and determining a second time T2 when a message waiting cycle is complete; and (5) ramping from said DC signal from said DC voltage level, beginning at said time T2, to said bias voltage level at a slope whose absolute value is less than the maximum absolute value of the slope of said AC signal.